1. Field of the Invention
This invention relates to laser oscillators and more particularly to a self-aligning, high-power laser oscillator for a free electron laser (FEL).
2. Description of the Prior Art
It is well known that free electron lasers are efficient sources of coherent, high power, tuneable radiation in the millimeter, far- and near-infrared, and visible wavelength regimes. The free electron laser (FEL), in its bare essentials, consists of a high-energy electron beam that, when properly phased, interacts with a superimposed laser beam in the transverse periodic magnetic field of a wiggler as considered in U.S. Pat. No. 3,822,410, issued to J. M. J. Madey. Typically the electron beam (e-beam) energy is many millions of electron volts, and its diameter a fraction of a millimeter. The length of the interaction region in the wiggler is several meters. Since the interaction occurs in such a small cross-sectional area but over several meters, this geometry results in a laser output with a power density which is extremely high. Laser output with peak power densities of several GW/cm.sup.2 are routinely obtained.
In prior art FEL's that rely on standard, stable optical resonators with conventional, material optics the incidence of such high flux densities on optics results in the coatings and/or their substrates having limited life. Also, the requirement for coalignment between the millimeter diameter e-beam and the laser beam is very critical. To minimize the incident power density on the mirrors through diffraction spreading of the beam the spacing between mirrors must be drastically increased. However, the alignment sensitivity of the resonator then increases dramatically to a point where the application of the stable resonator to a high power FEL becomes impractical.